This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present invention, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
As is well known, labels are commonly used in the decorating and/or labeling of commercial articles, such as, and without limitation, containers for beverages, essential oils, detergents, adverse chemicals, and health and beauty aids. One such type of label is a heat transfer label. Heat transfer labels are desirably resistant to abrasion and chemical effects in order to avoid a loss of label information and desirably possess good characteristics of adhesion to the articles to which they are affixed.
Heat transfer labels are multilayered laminates, with each layer having its own function. For example, heat transfer labels generally include an adhesive layer, an ink design layer, and a release layer. The release layer may be a wax release layer, and is often directly adjacent a carrier sheet, such as on a roll or web of labels. Thus, in such an example, the label may be thought to include a “support portion” (e.g., carrier sheet and release layer and a “transfer portion” (i.e., ink design layer and adhesive layer). When subjected to heat, the wax release layer softens, thereby allowing the transfer portion to be separated from the carrier sheet, and the adhesive layer adheres the ink design layer to an article being labeled. Alternatively, all or part of the wax release layer may transfer as well, to provide protection to the ink design layer. Additionally or alternatively, the labels may include a separate protective layer overlying the ink design layer to protect the ink design layer from abrasion.
More specifically, in the heat transfer labeling process, the label-carrying sheet is subjected to heat, and the label is pressed onto an article with the ink design layer making direct contact with the article. As the paper sheet is subjected to heat, the wax layer begins to soften so that the paper sheet can be released from the ink design layer. (And, as described above, a portion of the wax layer may be transferred with the ink design layer and a portion of the wax layer may remain with the paper sheet.) After transfer of the ink design layer to the article, the paper sheet is removed, leaving the ink design layer firmly affixed to the article. In an alternate embodiment, where the wax layer also transfers, the wax layer thus may serve two purposes: (1) to provide release of the ink design layer from the sheet upon application of heat to the sheet, and (2) to form a protective layer over the transferred ink design layer. After transfer of the label to the article, the transferred wax release layer may be subjected to a postflaming technique which enhances the gloss of the layer. Further, the presence of montan wax in the formulation also provides optical clarity to the layer (thereby enabling the ink design layer therebeneath to be better observed).
Thus, in general, many previous heat transfer labels for imprinting designs onto an article typically involve decorative laminates including a base sheet or web coated with a wax release layer over which a design is imprinted in ink. As is known to those of ordinary skill in the art, “wax” generally refers to a class of chemical compounds that are malleable near ambient temperatures. Characteristically, they melt above 45° C. to provide a low viscosity liquid. Waxes are organic compounds that are insoluble in water but soluble in petroleum-based solvents, and characteristically include long alkyl chains. Waxes may be natural or synthetic.
One disadvantage associated with the use of labels such as those described above is that the wax or waxes used in the release layers typically include a montan wax. Montan wax is a hard wax obtained by solvent extraction of certain types of lignite or brown coal. Its color ranges from dark brown to light yellow when crude, or white when refined. Its composition is non-glyceride long-chain (C24-C30) carboxylic acid esters (62-68 weight %), free long-chain organic acids (22-26%), long-chain alcohols, ketones, and hydrocarbons (7-15%), and resins having a melting range of about 82-95° C. One example of a montan wax that is used in wax release formulations is a partially saponified montan ester wax having an acid value in the range of 7-25 mgKOH/g, a dropping point in the range of 93° C.-110° C., a viscosity (at 120° C.) of 200-400, and a specific gravity in the range of 1.00 g/cm3-1.03 g/cm3. This montan wax may also have a penetrometer value of about 1. Such a wax is commercially available from Struktol Company of America (Stow, Ohio) under the name Struktol® Montan Wax OP. Another example of a release layer that includes montan wax-like release chemistry is disclosed in U.S. Pat. No. 4,557,964 (to Magnotta), the disclosure of which is hereby incorporated by reference herein in its entirety.
In general, when used with heat transfer labels (or other labels), montan wax imparts high gloss, hardness, and clarity into the release formulation and to the label. And these characteristics are very desirable in labels. Entities that produce labels (label manufacturers), and entities that use labels (the customers of those manufacturers), desire labels that have a clean, clear, and high gloss finish. Montan wax performs very well in these areas, and generally performs better than other types of wax used to date in the labeling industry.
Montan wax also does not suffer from the problem of “blushing,” which is a concern with other waxes. Blushing is the tendency of a wax to turn opaque following a post-flaming process. Once post-flamed, release layers that do not include montan waxes (e.g., release layers including paraffin and/or microcrystalline waxes) can become “cloudy” and opaque (at least in some areas), thereby ruining the aesthetic appearance of the label (as the portion of the release layer now overlies the transferred transfer portion of the label on an article). In particular, the label may appear “splotchy,” with some areas of the label appearing to have a matte finish, and other areas being shiny. When a release layer including montan wax is used (whether as a sole wax component, or in combination with other waxes), the “blushing” problem is reduced and eliminated.
And so, due to its performance characteristics, montan wax has been used in wax formulations for labels. It is generally a universal component used in release layers across the spectrum of labels.
However, there are drawbacks to the use of montan wax in release formulations. First, montan wax often undergoes degradation during the process of coating the wax release layer onto the carrier sheet, which causes the wax to yellow. More specifically, during the coating process, the montan wax needs to be heated so that it softens and becomes somewhat flowable so that it can be coated onto the carrier sheet (e.g., paper or a polymer film). However, the temperatures that are used during this coating process are high enough that the montan wax may begin to degrade. For example, the wax is generally heated to near 300° F. prior to application to the carrier sheet. However, at temperatures near or exceeding 300° F., the degradation and yellowing of montan wax begins. This detracts from the aesthetic appearance of the label in that the label can appear yellowed. This problem is magnified when the label is applied to a light background, such as a white container. Unfortunately, there are presently no substitute waxes that can provide all the benefits of montan wax at a comparable or cheaper price as montan wax. Thus, label manufacturers attempt to closely manage the coating temperatures in an attempt to prevent the yellowing of montan wax.
Further, as described above, montan wax is only available from a very few locations worldwide (including Amsdorf, Germany, and in the Ione Basin near Ione, Calif.). Presently, there is an ongoing shortage of montan wax that is affecting the world wide supply of the wax. Thus, the price of montan wax is subject to increases, which, in turn, increases the cost of labels including montan wax.
Thus, as described above, there are certain drawbacks to the use of release layers that include montan wax. Additionally, there are currently used release layers that do not include montan wax as a component of the release formulation. An example of such a formulation is disclosed in U.S. Pat. No. 4,536,434 (to Magnotta), the disclosure of which is hereby incorporated by reference herein in its entirety. However, these current non-montan wax release layers also suffer drawbacks. For example, as described above, the presence of montan wax in the release formulation provides a high gloss surface to the release layer once transferred with the transfer layer of the label to an article. This high gloss surface is aesthetically pleasing and is desired by many label customers. Unfortunately, the currently used release layers that do not include montan wax do not provide a high gloss finish. Rather they provide a matte (no-gloss) finish, and so are not a desirable or an effective substitute for release layers including montan wax.